I want to make a granny square of my down design. I've got 5 colors in mind and want the squares to be 8 to 10 inches. I'm not terribly concerned with overall size, but I'm thinking more of a throw for the sofa than a big blanket. The yarn I want to use is bulky weight (3.5oz/100g/135 yrd/123 m balls and the gauge is 9 sc & 12 rows = 4 inches with an 8mm hook).

Is there any way to tell from that information, roughly how much I would need for each color? Or am I out of my brain thinking I can figure this out without making a test square? I need to order the yarn online and they've got dye lot numbers of course.

This is the overall look I'm going for. (check out those mad photoshop skillz! )